The sequencing of human genome describes code sequences. Which region is a gene? What is the function? Which genes are needed for a biological function? How do they cooperate in normal life? Which mistakes are the causes for diseases? This difficult, challenging, beneficial, and profitable decoding works bring us into an era of functional genomics.
At the turn of the new century, the scientists deem that although the achievements of reproductive biology are great, the prospect of development is pessimistic if only the classic methods limited to tissues and cells are used without utilizing new technologies, without studying the molecular mechanisms, and without combining different disciplines. People have focused on female reproduction and paid little attention to male reproduction. The basic researches on reproductive principles are neglected, resulting in no ideal medicine and techniques for birth control and insufficient knowledge of human reproduction. The reproductive biology encounters two revolutionary changes in the 21st century. One is to strengthen the basic researches and study the mechanism for human reproduction and birth defects by using the new methods of molecular biology, molecular immunology and cell biology. The other is to strengthen the study of male reproductive biology, thereby developing male contraceptives.
China has 22% population, only 7% cultivated land and 6% fresh water in the world. Even the growth rate is 0.01%, 13 million peoples increase each year. The contraception methods, which are imperfect and have some side effects, are mainly used by females. The safe sterilization means are also taken by females. According to WHO statistics, only {fraction (1/12)} males in Sichuan province are vasoligated. Actually, both men and women have responsibility of contraception. The control of male reproduction is important to human quantity and quality because (1) a healthy man produces 108 sperms/day in 50 years and a woman produce 1 egg/month in 40 years, (2) the sperms are sensitive to environment, (3) the quantity and quality of sperm have decreased 40% in the last 50 years, and (4) 5-10% of males under 45 have primary sterility. To correct the bias, it is necessary to strengthen the researches and develop male contraception means. It is well-known that the health of human reproduction is important worldwide. The contraception is only a temporary measure for population crisis, and the off-springs should seek a physically and mentally healthy life. The design of birth-control medicine should suit the new needs. On Sep. 9-10, 1999, in the seminar of “male contraception in 21st century” held by NICHD in NIH headquarters, people studied the situation, put forward the objects and arranged the activities including co-operation and fund support [Trends in Endocrinology and Metabolism 2000, 11 (2):66-69].
Spermatocytes undergo mitosis, meiosis and differentiation and form sperms in testis. Then they enter into epididymis, gradually maturate in caput and corpus, and deposit at cauda until ejaculation. A series of maturation changes including the motor capacity of sperm, the formation of acrosome function, the conversion of metabolism are not accomplished by sperm themselves. The sperms gradually maturate by interacting with the epididymis micro-environment when passing the epididymis. Epididymis is a long, narrow and zigzag passage connecting testis and spermaductus. The cells in different parts of epididymis express different genes and products, and excrete different proteins and molecules. The different fluid components, ionic strength and pH form the changing micro-environment and interact with sperm to partially alter or modify the sperm surface protein, such as phosphorylation, esterification, acylation, carboxylation, and glycosylation. The sperms gradually obtain the functions and immunologic defense for maturation, which protect sperms in epididymis until they pass female genital tract toward ovum.
The maturation, storage and protection of epididymis have the following properties and, therefore, it is an ideal target for birth control.
(1) The function is simple. The interfering medicines are unlikely to cause severe side effects.
(2) Epididymis is a final organ for hormones and has no endocrine function. The epididymis medicines normally do not effect hormone secretion.
(3) Before entering epididymis, sperms are completely differentiated and transcription is stopped. The maturation involves protein modification but no DNA replication. The medicines are unlikely to cause DNA mutations and diseases.
(4) The study of epididymis is not emphasized and has promising potential.
The mechanism for forming the micro-environment in parts of epididymis is not determined by one or two genes and protein, but by a group of co-operating products. Little is known about the initiation and process of epididymis gene expression related to sperm maturation. The study helps to disclose the molecular mechanism of sperm maturation, decode genomic codes, establish a foundation for sperm-related infertility, and provide new routes for develop male contraception drugs which blocks sperm maturation.
Since 1970's, The researches on epididymis mainly focused on the following three aspects:
(1) Some results have been obtained on protein level by comparing the proteins in the lumen at different parts of epididymis or the differently maturated membrane proteins of sperm at different parts through dielectrophoresis, or by comparing them in immunoassay using polyclonal antibodies against proteins. However, the developments are dissatisfactory due to low sensitivity of separation or analysis technology. The Dacheux Laboratory (France) has reported the identification of more than 200 proteins from the lumen of epididymis of swine and sheep, indicating the research on epididymis is less difficult than the other organs. However, only 15 epididymis specific cDNAs have been cloned.
(2) The known roles of epididymis in sperm maturation may be used to determine whether the specific function of epididymis is related to some known proteins. For example, it is known that epididymis protects sperms from damage caused by oxygen free-radical. The mRNAs of six antioxidases on different parts of epididymis have been detected. E-GPX and E-SOD have the highest amount of mRNA at caput and corpus, respectively, indicating that the different parts of epididymis need different antioxidases. However, those researches are restricted to the known knowledge and hardly helpful to find new function genes or products. Additionally, there are many immunocytes and immuno-depressive molecules in epididymis, which forms a protecting immunological micro-environment. However, the molecules and cellular mechanism for the formation and regulation are unclear.
(3) The molecular biochemistry technology develops quickly since 1990's and one can find new genes specifically expressed in epididymis on mRNA level by subtraction hybridization, etc. A German laboratory found 6 new mRNAs in human epididymis by subtraction screening of cDNA library. However, due to the limitations of the human epididymis or other materials, their functions were not intensively studied. Therefore, people study the laboratory animals by different means.
Therefore, there is an urgent need to develop new natural protein related to male reproduction and epididymis.